03-04-2016, 06:01 PM
PM2 (and any others interested),
The reason the ISS appears to move so quickly compared to other satellites you may have seen is it's in low earth orbit (LEO) so it's not that far away when you see it and is actually traveling very quickly (17,000 mph). Other LEO satellites would appear to move as quickly, but are much smaller than the ISS therefore much fainter, and like the ISS can only be seen shortly after sunset or before sunrise, and are hard to spot with the naked eye, if not impossible. The satellites you see at night are in much higher orbit therefore farther away and are actually moving more slowly. The higher an object is in orbit, the slower it needs to move. Basically, people are not used to seeing fast-moving LEO satellites.
I might be wrong here, but I don't think flares from the ISS are easily predictable, I suspect it's because its structure is so complicated. However, there are things called Iridium flares you might want to watch for on your next early morning walk!
Iridium satellites (these are LEO communication satellites) have an unusual configuration of reflective antennas. They are controlled from the ground and the flares they produce are predictable, although their flares are a fairly narrow beam so even a few miles difference in locations on Earth makes a big difference to what you can see. The flares last for a few seconds but can be incredibly bright. They look like this:
https://youtu.be/uymzXNdXwmo
https://youtu.be/MTGVuPr9Epg
Heavens Above (http://www.heavens-above.com) is the best site I know for finding predicted flares. You'll need to set up your precise location (top right of the page) and then select Iridium Flares from the list on the left. I can't emphasize enough the need to get your location precise. You will get predictions for the next 10 days for flares you can see. The second column of the table (Brightness) will tell you how bright it will be in magnitudes. The more negative the number, the brighter it will be. Bear in mind this is a logarithmic scale, and Venus is typically about -4. So, if you get a flare prediction of, e.g., -7, that means it should appear roughly 15 times brighter than Venus.
If you're interested but need more info, just let me know.
ETA: Added another Iridium flare video
The reason the ISS appears to move so quickly compared to other satellites you may have seen is it's in low earth orbit (LEO) so it's not that far away when you see it and is actually traveling very quickly (17,000 mph). Other LEO satellites would appear to move as quickly, but are much smaller than the ISS therefore much fainter, and like the ISS can only be seen shortly after sunset or before sunrise, and are hard to spot with the naked eye, if not impossible. The satellites you see at night are in much higher orbit therefore farther away and are actually moving more slowly. The higher an object is in orbit, the slower it needs to move. Basically, people are not used to seeing fast-moving LEO satellites.
I might be wrong here, but I don't think flares from the ISS are easily predictable, I suspect it's because its structure is so complicated. However, there are things called Iridium flares you might want to watch for on your next early morning walk!
Iridium satellites (these are LEO communication satellites) have an unusual configuration of reflective antennas. They are controlled from the ground and the flares they produce are predictable, although their flares are a fairly narrow beam so even a few miles difference in locations on Earth makes a big difference to what you can see. The flares last for a few seconds but can be incredibly bright. They look like this:
https://youtu.be/uymzXNdXwmo
https://youtu.be/MTGVuPr9Epg
Heavens Above (http://www.heavens-above.com) is the best site I know for finding predicted flares. You'll need to set up your precise location (top right of the page) and then select Iridium Flares from the list on the left. I can't emphasize enough the need to get your location precise. You will get predictions for the next 10 days for flares you can see. The second column of the table (Brightness) will tell you how bright it will be in magnitudes. The more negative the number, the brighter it will be. Bear in mind this is a logarithmic scale, and Venus is typically about -4. So, if you get a flare prediction of, e.g., -7, that means it should appear roughly 15 times brighter than Venus.
If you're interested but need more info, just let me know.
ETA: Added another Iridium flare video